Here is a slideshow of the majority of my collection of tenkara flies. Most of these flies were gifts from tenkara anglers in Japan, and a large part of this collection was tied by Mr. Yoshikazu Fujioka who recreated historical tenkara flies he learned about in books and through hearsay.

The ones that have a long clear line are essentially snelled hooks with a heavy tippet at the end. In Japan it is very common to have eyeless hooks and this is a way to make an eye. I’d guess they are 3X. I am not sure what knot the original anglers would have preferred, but I’d likely use a loop to loop, this would allow me to change flies without cutting tippet.